Base sections

A synthetically useful reaction known as the Michael reaction, or Michael addition, involves nucleophilic addition of carbanions to a p unsaturated ketones The most common types of carbanions used are enolate 10ns derived from p diketones These enolates are weak bases (Section 18 6) and react with a p unsaturated ketones by conjugate addition... 

Conjugate base (Section 1 13) The species formed from a Brpnsted acid after it has donated a proton... 

Schiemann reaction (Section 22 17) Preparation of an aryl fluonde by heating the diazonium fluoroborate formed by addition of tetrafluorobonc acid (HBF4) to a diazonium ion Schiffs base (Section 17 10) Another name for an imine a compound of the type R2C=NR ... 

Strong base (Section 1 16) A base that is stronger than HO ... 

Weak acid (Section 1 16) An acid that is weaker than 1130" Weak base (Section 1 16) A base that is weaker than HO Williamson ether synthesis (Section 16 6) Method for the preparation of ethers involving an Sfj2 reaction between an alkoxide ion and a primary alkyl halide... 

International Pharmaceutical Service, CountyNatWestWoodMac, Data Base, Section 1, Monsanto U.S., Dec. 13,1991. 

The reaction of oxiranes with base can follow several paths, giving products of type (34-38 Scheme 27). (a) Formation of an oxiranyl anion (34) is rare (Section 5.05.3.5). (b) Nucleophilic ring opening to give (35) is common with unhindered bases (Section 5.05.3.4). (c) a-Elimination to give a carbene or carbenoid (36) is favored by alkyllithium bases and... 

An internal baffle in the base section to minimize hold-up... 

Section 4.6 Nonprocess Equipment Data Bases Section 4.7 Nonprocess Equipment Data Sources Section 4.8 Nuclear Probabilistic Risk Assessments (PRA)... 

Schiff s base (Section 17.10) Another name for an imine a compound of the type R2C=NR. ... 

Esters are usually prepared from carboxylic acids by the methods already discussed. Thus, carboxylic acids are converted directly into esters by SK2 reaction of a carboxyfate ion with a primary alkyl halide or by Fischer esterification of a carboxylic acid with an alcohol in the presence of a mineral acid catalyst. In addition, acid chlorides are converted into esters by treatment with an alcohol in the presence of base (Section 21.4). 

Esterification is normally carried out by treating the carbohydrate with an acid chloride or acid anhydride in the presence of a base (Sections 21.4 and 21.5). All the —OH groups react, including the anomeric one. For example, /3-o-glucopyranose is converted into its pentaacetate by treatment with acetic anhydride in pyridine solution. 

Bronsted-Lowry base (Section 2.7) A substance that accepts H+ from an acid. 

Lewis base (Section 2.11) A substance that donates an electron lone pair to an acid. All nucleophiles are Lewis bases. 

Schiff base (Sections 19.8, 29.5) An alternative name for an imine, R2C=NR. used primarily in biochemistry. 

Before dealing with electronic structures as such, it will be helpful to examine briefly the experimental evidence on which such structures are based (Section 6.1). In particular, we need to look at the phenomenon of atomic spectra, m... 

This shows that the pM value of the solution is fixed by the value of K and the ratio of complex-ion concentration to that of the free ligand. If more of M is added to the solution, more complex will be formed and the value of pM will not change appreciably. Likewise, if M is removed from the solution by some reaction, some of the complex will dissociate to restore the value of pM. This recalls the behaviour of buffer solutions encountered with acids and bases (Section 2.20), and by analogy, the complex-ligand system may be termed a metal ion buffer. 

J 1 Describe the chemical properties of acids and bases (Section J.l). 

When chemists see a pattern in the reactions of certain substances, they formulate a definition of a class of substance that captures them all. The reactions of the substances we call acids and bases are an excellent illustration of this approach. The pattern in these reactions was first identified in aqueous solutions, and led to the Arrhenius definitions of acids and bases (Section J). However, chemists discovered that similar reactions take place in nonaqueous solutions and even in the absence of solvent. The original definitions had to be replaced by more general definitions that encompassed this new knowledge. 

Because the concentrations of ions in a solution of a sparingly soluble salt are low, we assume, just as we did for solutions of weak acids and bases (Section 10.7), that we can approximate Ksp by... 

What Do We Need to Know Already This chapter draws on many of the principles introduced in the preceding chapters. In particular, it makes use of the electron configurations of atoms and ions (Sections 1.13 and 2.1) and the classification of species as Lewis acids and bases (Section 10.2). Molecular orbital theory (Sections 3.8 through 3.12) plays an important role in Section 16.12. 

MRL users should be familiar with the toxicological information on which the number is based. Section 2.4, "Relevance to Public Health," contains basic information known about the substance. Other sections such as 2.6, "Interactions with Other Chemicals" and 2.7, "Populations that are Unusually Susceptible" provide important supplemental information. 

With this goal in mind, we have studied the reaction of silica with a Lewis acid, such as AlBuj, B(CsF5)3, B(C5F5)j, in presence of a Br0nsted base (Section 2.1). We... 

A tertiary base isolated from Thalictrum strictum was assigned a pavine structure based on the spectral data (27). Three methoxyl and one methylenedioxy functions were detected with the aid of mass spectroscopy. Structure 3 was proposed as the most probable representation for this new pavine alkaloid, which indeed is the first example of a pentasubstituted pavine base. However, when the reported aromatic proton chemical shifts (8 6.23, 6.36, and 6.54) were evaluated in the light of empirical rules about the H-NMR absorptions of pavine bases (Section V,B), and it seemed possible that the two upfield absorptions belong to H-4 and H-10 rather than to H-1 and H-10. Therefore, alternative structure 4 cannot presently be completely excluded from consideration. 

Dimroth rearrangement probably starts with a covalent hydration catalyzed by acids or bases (Section II,B,3). According to Dukes et al. [72JCS(P2)1695] there is evidence from pKa values, kinetic measurements, and UV spectra that the alkaline hydrolysis of the amine 46 includes intermediate 47 (Scheme 22). 

---